This invention relates to an air-release valve, of the type which is commonly used in a system containing liquid with gas above it. A common use of such a valve is for the release of gases from sewage systems during flow conditions, as distinct from the conditions which obtain during the charging and discharging of a pipeline or container.
Previously, a valve of this type has had a single orifice for the release of gas, the orifice being opened or closed either by a float, usually a rubber-covered sphere, or alternatively by a linkage mechanism interposed between the orifice and the float, and operated by the float.
A disadvantage of the former type of valve is that the level of liquid in relation to the ball is fairly high, with the result that the orifice may be fouled by the liquid or any floating debris in the pipeline. Also, when such a valve is closing during the charging of a pipeline or container, the high level of liquid relative to the ball may result in a quantity of the liquid being ejected from the valve orifice. In normal operation, the use of a fixed orifice results in the orifice seating bleeding continuously as the air and gases accumulate, and this continuous bleeding can erode and wear the orifice and the surface of the ball or float.
In the latter type of valve mentioned, the linkage mechanism is likely to become fouled by the liquid or floating debris, causing malfunction of the valve and the release of contained liquid. Also, such a linkage is liable to wear, reducing the efficiency of control and gas release.
In either form of air-release valve hitherto used, there is a likelihood of fumes and odours escaping from the pipeline when the line is draining or in a drained condition.
The present invention has been devised with the general object of overcoming the said present disadvantages by providing an air-release valve which will operate efficiently, is not liable to malfunction as a result of fouling from debris, and which is efficiently sealed when a pipeline or container is draining or in a drained condition.